Installation of "water jets," or electrically cooled large water dispensers, in elementary and middle schools was linked to a small but statistically significant decline in mean body mass index among students, a large "quasi-experimental" study of New York City schools found.

Compared with a pre-installation baseline, mean BMI was lower by 0.025 points (95% CI -0.038 to -0.011) in boys and by 0.022 points in girls (95% CI -0.035 to -0.008) in schools that installed the water dispensers, after adjusting for changes seen in other schools that did not have the dispensers, reported Amy Ellen Schwartz, PhD of Syracuse University in Syracuse, N.Y., and colleagues.

Students were also less likely to become overweight following adoption of the water dispensers. Risk of becoming overweight was lower by 0.9 percentage points in boys (95% CI -0.015 to -0.003, P<0.01) and by 0.6 percentage points in girls (95% CI -0.011 to 0.000, P<0.05), again after adjusting for changes in nonparticipating schools, the authors wrote in JAMA Pediatrics.

Co-author Brian Elbel, PhD, of NYU School of Medicine in New York City, characterized the impact of these water jets on student weight as "small, but meaningful" especially given that 40% of public school children are overweight.

"In the scheme of things, these are real changes particularly for such a low-cost intervention," he told MedPage Today. "If this thing really is working, it should be easy to do in lots of different schools."

These water dispensers even appeared to affect milk sales in the cafeteria, with significant decreases seen for plain and chocolate-flavored products.

Skylar Griggs, MS, RD, LDN, clinical nutrition specialist for the preventative cardiology division at Children's Hospital in Boston, who was not involved in the study, suggested that the reduction in milk sales may explain the effects on BMI.

"I was not shocked by the BMI reduction observed in this study, as it was noted that inclusion of the water bubbler meant less chocolate milk consumption," Griggs wrote in an email to MedPage Today. "Chocolate milk may still be milk, but if you break it down by sugar, it contains 5 packets of sugar in 1 serving."

She also applauded the return of attention to water dispensers in schools.

It's not a new intervention in the context of fighting child obesity, as access to drinking water in the cafeteria was part of the Healthy, Hunger-Free Kids Act of 2010. But an accompanying editorial by Lindsey Turner, PhD, of Boise State University in Idaho, and Erin Hager, PhD, of the University of Maryland in Baltimore, said that schools had only fulfilled that requirement through the presence of a drinking fountain. They add that while water dispensers are only around $1,000, it still may be a stretch for the budget of some school districts.

"A school-based drinking water access intervention can be remarkably affordable relative to other, more intensive obesity strategies," Turner and Hager wrote. "[But] even fairly low costs of water dispensers may pose a barrier to implementation and sustained access to water in schools, particularly given the many worthy and competing demands for limited budgetary resources in many educational agencies."

Schwartz's team examined data from 1,227 New York public elementary and middle schools from 2008-2009 to 2012-2013. Individual BMI data was derived from New York's FITNESSGRAM program, which annually measures the height and weight of students. The water dispenser program began with a pilot of five school cafeterias, and by the end of the study period, it was in two-thirds of examined schools. Ultimately, data for more than 1 million children were analyzed in the study.

The authors note two important limitations to the findings. Administrative data was used for both water jet delivery and milk purchases, as opposed to observing actual use of water dispensers and measuring actual milk consumption, respectively.

They also cite the lack of data on which beverages students were actually consuming, which Elbel saw as an opportunity for future research.

"New York City did a really great job of eliminating sugar-sweetened beverages in schools even before our study, but I think it would be really interesting to see in a school district that hasn't done that -- would you even imagine a bigger effect there?" he said. "I think it would be interesting to see what sort of effect they might see."

This study was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

The study authors and editorialists disclosed no conflicts of interest.